Optical and computed evaluation of keyhole diffractive imaging for lensless x-ray microscopy

摘要

X-ray microscopy without the need to focus the x-rays is obviously desirable. Thus, various ways of reconstructing the image frpm the far-field diffraction pattern have been demonstrated during the last decade. Here, the authors describe a variant of keyhole diffractive imaging in which the knowledge of the illuminating wavefront is used in the reconstruction. Unlike prior work in keyhole imaging in which a diverging beam was used, the authors employ a collimated beam such as emerges from a free electron x-ray source. From both computer simulations and scaled optical experiments, the authors found that the reconstruction is best when the shape is a right-angled triangle. For the authors' samples, the best size of the triangle is one that covers about half of a rectangle 3000 X 3000 wavelengths. If the area is smaller, then the time to cover the entire sample is too long; if larger, then the reconstruction takes far longer and results in a noisy image. From the authors' scaled experiment conducted under blind conditions (no a prior knowledge of the sample), it appears that a resolution of 10 nm should be readily achievable at an x-ray wavelength of 0.18 nm.